A vacuum pump includes a casing that forms a casing including an inlet port and an outlet port, and a structure for causing the vacuum pump to exhibit an exhaust function is housed in the casing. The structure for causing the vacuum pump to exhibit the exhaust function is roughly configured from a rotatably axially supported rotor portion and a stator portion fixed to the casing.
A motor for rotating a rotating shaft at high speed is provided. When the rotating shaft rotates at high speed according to the function of the motor, gas is sucked from the inlet port and discharged from the outlet port according to interaction of a rotor blade (a rotating disk) and a stator blade (a stator disk).
Among vacuum pumps, a Seigbahn type molecule pump having a Seigbahn type configuration is a vacuum pump including a rotating disk (a rotating disc) and a stator disk set to have a gap (a clearance) from the rotating disk in the axial direction. A spiral groove (also referred to as helical groove or swirl-like groove) channel is engraved on a gap-opposed surface of at least one of the rotating disk and the stator disk. The vacuum pump gives, with the rotating disk, a momentum in a rotating disk tangential direction (i.e., a tangential direction of a rotating direction of the rotating disk) to gas molecules diffusing and entering the spiral groove channel to give dominant directivity from an inlet port to an outlet port and perform exhaust.
To industrially use the Seigbahn type molecular pump or a vacuum pomp including a Seigbahn type molecular pump portion, rotating disks and stator disks are formed in multiple stages because a compression ratio is insufficient when the stage of the rotating disk and the stator disk is single.
However, the Seigbahn type molecular pump is a radial flow pump element. Therefore, in order to achieve the multiple stages, a configuration is necessary in which a channel is turned back at outer circumferential end portions and inner circumferential end portions of the rotating disks and the stator disks from the inlet port to the outlet port (i.e., in the axial direction of the vacuum pump) to, for example, exhaust gas from an outer circumferential portion to an inner circumferential portion, thereafter exhaust the gas from the inner circumferential portion to the outer circumferential portion, and exhaust the gas from the outer circumferential portion to the inner circumferential portion again.
Japanese Patent Application Laid-Open No. S60-204997 describes a technique for, in a vacuum pump, providing a turbo molecular pump portion, a helical groove pump portion, and a centrifugal pump portion in a pump housing.
Japanese Utility Model Registration No. 2501275 describes a technique for, in a Seigbahn type molecular pump, providing spiral grooves in different directions on opposed surfaces of rotating disks and stationary disks.
A flow of gas molecules (gas) in the configuration of the related art is as explained below.
Gas molecules transferred to an inner diameter portion in an upstream Seigbahn type molecular pump portion are discharged to a space formed between a rotating cylinder and the stator disk. Subsequently, the gas molecules are sucked by an inner diameter portion of a downstream Seigbahn type molecular pump portion opened in the space and transferred to an outer diameter portion of the downstream Seigbahn type molecular pump portion. When the rotating disks and the stator disks are formed in the multiple stages, this flow is repeated in each of the stages.
However, the space (i.e., the space formed between the rotating cylinder and the stator disk) does not have exhaust action. Therefore, a momentum in an exhaust direction given to the gas molecules in the upstream Seigbahn type molecular pump portion is lost when the gas molecules reach the space.
FIG. 12 is a diagram for explaining a conventional Seigbahn type molecular pump 1000 and is a diagram showing a schematic configuration example of the conventional Seigbahn type molecular pump 1000. Arrows indicate a flow of gas molecules.
FIG. 13 is a diagram for explaining a stator disk 5000 disposed in the conventional Seigbahn type molecular pump 1000 and is a sectional view of the stator disk 5000 viewed from an inlet port 4 side. Arrows inside the stator disk 5000 indicate a flow of gas molecules. An arrow outside the stator disk 5000 indicates a rotating direction of a rotating disk not shown in the figure.
Note that, in the following explanation, the inlet port 4 side of one (one stage of) stator disk 5000 is referred to as Seigbahn type molecular pump upstream region and an outlet port 6 side is referred to as Seigbahn type molecular pump downstream region.
As explained above, in the Seigbahn type molecular pump 1000, even if a dominant momentum toward the outlet port 6 is given to the gas molecules, since an inner turning-back channel “a” (i.e., a space formed between a rotating cylinder 10 and the stator disk 5000), which is a channel of the gas molecules, is a “connection” space not having exhaust action, the given momentum is lost. Therefore, since the exhaust action is interrupted in the inner turning-back channel “a”, the compressed gas molecules are released every time the gas molecules pass the inner turning-back channel “a”. As a result, satisfactory exhaust efficiency is not obtained in the conventional Seigbahn type molecular pump 1000.
If the channel cross-sectional area of the inner turning-back channel “a” is reduced (i.e., a gap formed by the outer diameter of the rotating cylinder 10 and the inner diameter of the stator disk 5000 is narrowed) by, for example, reducing dimensions, the gas molecules are held up in the inner turning-back channel “a” and a channel pressure of the inner turning-back channel “a”, which is an outlet (a turning-back point from an upstream region to a downstream region) of the Seigbahn type molecular pump upstream region, rises. As a result, a pressure loss occurs and the exhaust efficiency of the entire vacuum pump (Seigbahn type molecular pump 1000) is deteriorated.
In order to prevent the deterioration in the exhaust efficiency, conventionally, as shown in FIG. 12, the channel cross-sectional area and the conduit width of the inner turning-back channel “a” need to be secured sufficiently larger than the cross-sectional area and the conduit width of a conduit (which is a gap formed by opposed surfaces of the rotating cylinder 10 and the stator disk 5000 and is a tubular channel through which the gas molecules pass) in the Seigbahn type molecular pump portion.
However, if the dimensions of the channel of the inner turning-back channel “a” are set large, the inner diameter side is limited by the dimensions of, for example, a radial direction magnetic bearing device 30 that supports a rotating portion. On the other hand, if the diameter of the stator disk 5000 on the outer diameter side is increased, the radial direction dimension of the Seigbahn type molecular pump portion decreases and the channel is narrowed. As a result, compression performance per one stage is not sufficiently obtained.
In order to obtain a predetermined compression ratio using the related art, it is necessary to increase the number of stages of the Seigbahn type molecular pump portion. However, when the number of stages is increased, material expenses and machining expenses of the rotating disk 9 and the stator disk 5000 increase. Further, the mass inertia moments of the rotating disk 9 rotating at high speed increase, and the capacity of the magnetic bearing device supporting the rotating disk 9 needs to be increased correspondingly. As a result, costs of components configuring the vacuum pump increase.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.